The present invention generally relates to multi-point conference systems, and more particularly to a multi-point conference system which enables a video conference to be made simultaneously among three or more stations.
A video conference is made among distant locations in order to quickly transmit information and to reduce both time and cost of business trips and of moving objects. Presently, a conference (communication) is made between two stations on a point-to-point basis as shown in FIG.1. Each station, that is, each conference room, includes a panoramic camera 11 for picking up a panoramic view of the conference room, a close-up camera 12 for picking up a person (for example, a speaker), a camera 13 for picking up a material used in the conference, a monitor 14 for displaying a received image, a monitor 15 for displaying a transmitting image, a microphone 16, a speaker 17 and a console 18 which are all connected to a conference control unit 20.
The conference control unit 20 controls the input/output of input image data from the cameras 11 through 13 and output image data to the monitors 14 and 15. The conference control unit 20 also controls the coding/decoding of the image data and the audio data, and controls the multiplexing/demultiplexing of the image and audio data. The control operation of the conference control unit 20 realizes an interactive conference between two stations. However, there are demands to realize a multi-point conference system which enables a conference among three or more stations.
As a multi-point conference system which enables a conference among three or more stations, there is a conventional system shown in FIG.2 in which a circuit is connected to all of stations 10. However, as the number of stations 10 increases, the number of circuits also increases. When the number of stations 10 is denoted by n, the number of circuits becomes .SIGMA.i, where i=1, 2, . . . , n-1. As a result, each station 10 must have the conference control unit 20 shown in FIG.1 with a number of coder/decoder parts corresponding to the number of stations 10 connected thereto.
On the other hand, it is conceivable to connect the circuits in a star connection by use of a center unit 30 as shown in FIG.3. In this case, the center unit 30 selectively distributes the image data to the stations 10. But in this case, the center unit 30 must switch the image data depending on control signals which are received from each of the stations 10. As a result, there is a problem in that the required image data must be manually requested from each of the stations 10, and it is difficult to smoothly and efficiently make the video conference.